Blender wont import fbx animations correctly (Mixamo)
I found that importing the FBX with skin fixes the problem. I hope this helps.

If you export a binary FBX from Blender to Mixamo and get the expected results next thing is to download the FBX with animation and skin. What is usually done is to import all other animations without any skin. There is where I found the problem if The animation is downloaded without skin It wont re-target correctly.